Problem: A group of adults and kids went to see a movie. Tickets cost $$5.00$ each for adults and $$4.50$ each for kids, and the group paid $$56.00$ in total. There were $4$ fewer adults than kids in the group. Find the number of adults and kids in the group.
Answer: Let $x$ equal the number of adults and $y$ equal the number of kids. The system of equations is then: ${5x+4.5y = 56}$ ${x = y-4}$ Solve for $x$ and $y$ using substitution. Since $x$ has already been solved for, substitute ${y-4}$ for $x$ in the first equation. ${5}{(y-4)}{+ 4.5y = 56}$ Simplify and solve for $y$ $ 5y-20 + 4.5y = 56 $ $ 9.5y-20 = 56 $ $ 9.5y = 76 $ $ y = \dfrac{76}{9.5} $ ${y = 8}$ Now that you know ${y = 8}$ , plug it back into ${x = y-4}$ to find $x$ ${x = }{(8)}{ - 4}$ ${x = 4}$ You can also plug ${y = 8}$ into ${5x+4.5y = 56}$ and get the same answer for $x$ ${5x + 4.5}{(8)}{= 56}$ ${x = 4}$ There were $4$ adults and $8$ kids.